JPH044563B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an autofocus device for a video camera.

Traditionally, focus devices installed in video cameras measure the distance between the camera and the subject using the principle of triangulation, such as the so-called double image matching method, and then adjust the lens to focus on the measured distance. A method is adopted in which the front lens is moved by a motor to a pre-calibrated position on the distance axis.

This method or a similar method can usually obtain an autofocus function for subjects at a distance of 1 m to ∞, but when the subject is less than this distance, for example, only a few centimeters from the lens, close-up photography, so-called macro photography, is possible. is powerless.

There are three main reasons why this method cannot perform autofocus during macro photography.

(1) In triangulation or similar methods, the number
Accurate distance measurement over a large distance range from cm to ∞ is not possible.

In other words, the triangulation method uses the deflection angle of the mirror to correspond to the distance and is calibrated.
To measure ∞, the deflection angle width of the mirror needs to be several tens of degrees, which is an unrealistic value.

(2) For objects that are several centimeters away, the variation between the triangulation unit and the lens increases, and the probability that the measured distance is not necessarily the distance to the object to be imaged increases significantly.

(3) Autofocus devices focus by controlling the rotation of the distance ring on the front element of the lens, but since focusing in the macro area is usually done using a zoom ring, autofocus devices focus only in the macro area. Unable to focus.

In principle, these reasons seem to be solvable by using ultra-high precision mirror shake angle calibration control, parallax correction means, and control by sending an autofocus signal to the zoom ring, but at present. This is nearly impossible to achieve, as evidenced by the fact that some proposals have been made to disable the autofocus function during macro photography.

Also, as described in Japanese Patent Application Laid-Open No. 49-115322,
When installed in front of the focusing lens,
The shorter the subject distance, the greater the amount of focusing lens extension, so the size of the lens section limits the closest distance.On the other hand, if it is placed at the rear, the limitations due to the size of the lens section are resolved. However, the adjustment itself is difficult because the amount of movement of the focusing lens depends on both the subject distance and the zoom magnification.

SUMMARY OF THE INVENTION In view of the above-mentioned prior art, an object of the present invention is to provide an autofocus device for a video camera that is capable of macro photography.

The present invention has a master lens that is placed at the rear of the lens system and is movable back and forth within a predetermined movable range, and a zoom lens whose zoom magnification is variable within a predetermined range; A camera circuit includes an image sensor that converts an optical image obtained from a lens into an electrical signal, and a signal processing circuit that processes the electrical signal to obtain a video signal, and performs vertical scanning based on the video signal output from the camera circuit. A focus amount detection circuit that detects the degree of focus accuracy every cycle, a driving means that moves the master lens back and forth, and a position of the master lens via the driving means according to the degree of focus accuracy detected by the focus amount detection circuit. a first state in which the master lens is movable over the entire predetermined movable range over the entire predetermined range in which the zoom magnification can be changed; The larger the magnification, the more the master lens's movable range is restricted, and the second state is such that the closest focusable distance at the closest end of this restricted movable range is kept constant regardless of the zoom magnification. Either one is provided with switching means for switching the movable range of the master lens, so that the operator of the video camera can switch between the first state, which allows automatic focusing up to extremely close range, and the zoom state, depending on the usage situation. It is possible to switch between the second state, which is similar to a conventional automatic focusing camera, in which the closest focusing distance remains constant even when the magnification changes.

An embodiment of the present invention will be described below with reference to the system configuration block diagram shown in FIG. 1 and the characteristic diagram shown in FIG. 2.

In FIG. 1, reference numeral 1 denotes a zoom lens, which has a structure that enables focusing by moving part or all of a master lens.

2 is a camera circuit consisting of a video camera image sensor, a signal processing circuit, etc.; 3 is a focus amount detection circuit; 4
5 is a differential detection circuit, 5 is a motor drive circuit, 6 is a motor that drives the focusing structure of the zoom lens 1, and 7 is rotated in conjunction with the zoom lever to detect the zoom position of the zoom lens 1, that is, the focal length. 8 is a movement range calculation circuit; 9 is a lens position detector for detecting at what distance the focusing structure is properly aligned; 10 is a zoom position detector such as a potentiometer; This is a push button switch for setting whether to perform autofocus operation in the normal distance range or macro range operation.

First, a case will be described in which the structure shown in the figure performs an autofocus operation in a normal distance range, for example, a close range of 1 cm to ∞ using the push button switch 10. A subject image incident on a zoom lens 1 is converted into a captured video signal by a camera circuit 2 and inputted to a focus amount detection circuit 3. The focus amount detection circuit 3 detects the amount of the high frequency component of the imaged video signal corresponding to the focus condition of the screen during shooting, that is, the sharpness of the screen link, at each screen period, for example, every 1/60 second. It is input to the difference detection circuit 4. Therefore, if the motor drive circuit 5 operates the above function while moving the focusing structure of the zoom lens 1 using the motor 6, the output of the difference detection circuit 4 will indicate that if the rotational direction of the motor 8 is the direction in which the focus is being focused. If then positive,
On the other hand, if the focus is blurred in any direction, a negative voltage output is obtained. If this output is positive, the rotational direction of the motor 8 is kept as it is, and if it is negative, the rotational direction of the motor 8 is reversed. It can be seen that the configuration shown in FIG. 1 constitutes an autofocus device. What should be noted here is that focusing of zoom lens 1 is performed by moving part or all of the master lens system, and in this case, the position of the master lens and the subject that is in focus at that position are As shown in A, B, and C in Figure 2, the distance for objects at ∞ distance is a constant value regardless of the zoom magnification (A in the figure), but for other distances (close-up distance of 1 m, H in the figure) In the case of 2 m, it depends on the zoom magnification, that is, the focal length, of the zoom lens 1, as shown in B in the figure.In other words, when the focal length is the maximum (the zoom magnification is maximum), for example, the value of A2 in the figure, The movement range of the master lens position to focus on a subject within the normal distance range of 1 m to ∞ is 0 to _B2 in the same figure, but the focal length is the minimum (minimum zoom magnification), for example in the same figure. When the value of A is ₁ , the movement range of the master lens position to cover the same distance range can be as small as 0 to B ₁ in the figure.The difference in movement range due to this difference in focal length is almost the same as that of a zoom lens. It is proportional to the square of the zoom magnification of 1.In other words, in the case of a 6x zoom lens, the difference in movement range is approximately 36x, and this difference is due to the movement of the subject during imaging or the panning operation of the camera. In order to minimize movement in the blurring direction due to misjudgment of the motor movement direction due to malfunction of the difference detection circuit 6, etc., in autofocus operation in the normal distance range,
The focal length is detected by the zoom position detector 7 linked to the zoom ring of the zoom lens 1, and the master lens position is determined by inputting this into the movement range calculation circuit 8 which incorporates the characteristics shown in FIG. 2 as a calculation formula or table. The motor 6 is controlled via the motor drive circuit 5 while referring to the output of the lens position detector 9 that detects the lens position, and the movement range of the focusing structure of the zoom lens 1 is kept within the minimum necessary value range. good.

In addition, in this case, as shown in FIG. 2 as the movable area of the zoom lens 1 as Y, the closest distance that can be focused is a constant value of 1 m regardless of the zoom magnification. It has the same operating characteristics as a conventional front-element focus type camera in which the closest possible distance is constant, so even people who are used to operating conventional cameras will not feel any discomfort.

Next, when the configuration shown in FIG. 1 operates as an autofocus device in the macro range, that is, several centimeters to 1 meter (in other words, a distance longer than that) using the push button switch 10, the zoom lens 1 movable area) will be explained. When focusing is performed by moving the master lens as in zoom lens 1, so-called macro operation is possible at any focal length, but for the sake of simplicity, the focal length is set to the minimum value A ₁ , that is, the zoom magnification. The case where is the minimum will be explained. When the focal length is A ₁ , for shooting in the normal distance range,
As mentioned above, the movement range of the master lens can be limited to 0 to _B1 , but conversely, the movement range is not limited to this,
Set the movement range when the zoom magnification is at its maximum value from 0 to B ₂
In this case, the distance range in which focusing is possible is approximately the normal distance range (close range for focusing/zoom magnification squared) to ∞, that is, when the close distance is 1 m and the zoom magnification is 6 times, it is approximately 2.8 cm to ∞. In other words, when autofocus operation in the macro area is specified by the push button switch 10, by setting the master lens movement range of the movement range calculation circuit 8 from 0 to _B2 , the configuration shown in FIG. Continuous autofocus operation is possible without switching over the entire range.

As explained above with reference to FIGS. 1 and 2, according to the present invention, autofocus is performed in both the normal distance range and the macro range by changing the movement range of the master lens position by opening and closing the push button switch 10. I can do it. In the above explanation, autofocus operation in the macro range was explained for the case of the minimum focal length, but even if the focal length is a different value, the closest distance during macro operation becomes larger as the focal length increases. It is clear that a similar function can be obtained by allowing it to develop.

In addition, in the above explanation, the master lens movement range during macro operation was set to 0 to B ₂ , making it possible to focus up to infinity, but the lower limit of the movement range was set to 0.
It is also possible to reduce malfunctions of autofocus during macro operation by narrowing the movement range of the lens by setting it to a finite value.

Further, in the above explanation, the push button switch 10 can be opened and closed regardless of the focal length, but in home video cameras and the like aimed at general consumers, the push button switch 10 is used to improve operability by simplifying operations.
It is also good to have a structure in which the zoom lever can only be opened and closed within a specific value or range. Further, although the above description did not specifically explain the variable power structure of the zoom lens 1, this may be a normal variable power mechanism or may have a so-called macro function.

Additionally, an operation switch for directly rotating the motor 6 may be added to the configuration shown in Fig. 1 to enable manual focusing. In this case, it is necessary to have both a manual and automatic switching switch. Needless to say, there is.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of an autofocus device for a video camera according to the present invention, and FIG.
The figure is a characteristic diagram for explaining the operation. 1: Zoom lens, 2: Camera circuit, 3: Focus amount detection circuit, 4: Difference detection circuit, 5: Motor drive circuit, 6: Motor, 7: Zoom position detector, 8:
Movement range calculation circuit, 9: Lens position detector, 1
0: Push button switch.

Claims (1)

[Claims] 1. A master lens disposed at the rear of the lens system and movable back and forth within a predetermined movable range;
A zoom lens whose zoom magnification is variable within a predetermined range, an image sensor placed behind the master lens that converts an optical image obtained from the zoom lens into an electrical signal, and a signal that processes the electrical signal to obtain a video signal. A camera circuit consisting of a processing circuit, a focus amount detection circuit that detects the degree of focus accuracy for each vertical scanning period based on the video signal output from the camera circuit, a driving means for moving the master lens back and forth, and a focus amount detection circuit. A focusing means controls the position of the master lens for focusing via a driving means in accordance with the degree of focus accuracy detected by the circuit, and a focusing means controls the master lens over a predetermined range in which the zoom magnification can be changed. The first state is movable over the entire predetermined movable range, and the larger the zoom magnification is, the more the movable range of the master lens is restricted, and focusing is possible at the closest end of this limited movable range. a switching means for switching the movable range of the master lens between a second state in which the closest distance is constant regardless of the zoom magnification; scum device. 2. The autofocus device for a video camera according to claim 1, wherein the focus amount detection circuit detects the degree of focus accuracy based on the amount of high frequency components of the video signal. 3. In the second state switched by the switching means, the movable range of the master lens is limited depending on the longitudinal position of the master lens and the zoom magnification. An autofocus device for a video camera as described in Section 1.